The film begins with Samar Anand (Shahrukh Khan) a major from the Indian Army, defusing a bomb. After a while, Akira Rai (Anushka Sharma), a Discovery Channel intern, dives in a cold river in Ladakh because of a bet. As soon as she got into the river, she felt so cold that she started drowning and cried for help. Samar saves her and gave his jacket to warm her. Akira, offended by his late reaction, starts yelling at him. After reaching her hotel, she finds out a diary which falls from the jacket''s pocket. Curious, she starts reading it.
Samar, aged 28, was a struggling immigrant in London, working as a street musician and a seafood seller. He was offered a job to be a part-time waiter in a hotel, which he accepted. One day, he meets Meera (Katrina Kaif) in her engagement party taking place at his hotel. Meera believed that giving up something she loves is the only way to ask for a favour. In exchange for some English lessons, Samar agreed to teach Meera a Punjabi song. In the process, Samar fell in love with Meera. Samar helped Meera get out of her shell & also in resolving her issues with her mother which made Meera reciprocate his feelings. On the day when Meera was going to tell her father about their relationship, Samar is hit by a car and goes unconscious. Meera starts praying to God to save Samar and makes a vow to never meet him again. Soon, Samar makes a speedy recovery. Samar comes to know about the vow and in anger, tells her to go away and leaves London, giving all his money to his roommate. Samar challenges God to keep him alive while he will risk his life everyday because he believes his death is the only way to make Meera lose her faith in the deity who stole his love. He goes to India and gets a job as an army officer posted in Kashmir.
As Akira finishes reading the diary, she requests her boss to make a documentary about the bomb disposal squad of the Indian Army, and is granted permission. She approaches Samar and his colleagues for help and soon gets acquainted with them. She soon starts showing romantic feelings towards Samar, though he refuses reciprocation due to his past. Akira makes the film successfully and departs for London, earning her praise from her boss but to launch it, she needs Samar to come to London. After extensively persuading an overly hesitant Samar to come with her, he again gets hit by a car and is diagnosed with Retrograde amnesia, remembering only the events before his former accident. Akira meets Meera to help her try and recover Samar''s memory, but she is hesitant as Meera is happy with her own family. Later, it is revealed that Meera never married her fiancé as she loved Samar too much. Meera pretends to be Samar''s wife to recover his memory and Samar is told that he is the owner of a big restaurant. During this time, Akira realizes that Major Samar is only a fragment of young Samar who was a jubilant social man while today''s is a lonely bitter individual. Later, he comes across a